Week 10 Bioscience Flashcards
Nose & Nasal Cavity
Nose
* Facilitates smell
* Hairs - filter
Nasal conchae
* Increased surface area
* Warm and humidify air
* Enhance air turbulence
Mucosal epithelium
- Produces mucus humidifies incoming air traps particulates contains antibacterial compounds (lysozyme and defensins)
- bears cilia - moves contaminated mucous to the throat
Pharynx
- Passageway for air and food
Larynx
- Open passageway for air to reach the trachea
- Arrangement of cartilages
- Routes food and air into the correct passageways
Trachea
- Windpipe
- C-shaped cartilage rings
- Mucociliary escalator
Lungs
- Lie within the thoracic cavity - pleural cavities
- Left lung – 2 lobes ; Right lung – 3 lobes
- Large, soft and spongy organs – highly elastic
The Lungs & pleura
Pleural fluid
* within the pleural space
* acts as a lubricant
* adheres lungs to the thoracic cavity wall
Adherence of the two pleural membranes to one another is absolutely essential for normal breathing
The Respiratory Tree
- Branching network of airways starting from the trachea
Conducting Zone
- Airways become smaller: diameter decreases
- Mucociliary escalator disappears
- Cartilage rings - cartilage plates
- Gain smooth muscle tissue and elastic fibres
The Respiratory Zone
The respiratory zone is the only site of gas exchange.
* Alveolar sacs and alveoli are surrounded by capillaries
* The respiratory membrane
* Formed where the alveoli contacts the capillary
* Site of gas exchange
Alveoli
- Alveolar pores connect neighbouring alveoli
- Type I alveolar epithelial cells form the major part of the alveolar walls
- Type II alveolar epithelial cells are scattered among the type I cells and produce surfactant
- Alveolar macrophages crawl around the alveolar surfaces to consume bacteria, dust and debris
The Respiratory Membrane – the site of gas exchange
- formed where the Type I alveolar epithelial cells contact the capillaries
- formed where the Type I alveolar epithelial cells contact the capillaries
- Very thin (0.5µm wide)
- Efficient gas exchange
- Alveolar surface is coated with alveolar fluid
- Prevents damage
- Facilitates gas exchange
- Surfactant – prevents alveolar collapse
Blood supply to the lungs
Blood ENTERS the lungs via 2 circulations:
1.Pulmonary circulation
* pulmonary arteries deliver blood requiring oxygenation
* nutrients for alveoli
2. Bronchial circulation
* bronchial arteries provide oxygenated blood to rest of the lung tissue
Blood LEAVES the lung via 1 circulation:
1. Pulmonary circulation
* Pulmonary veins return blood to the heart
Innervation of the lungs
- Sensory fibres
* Degree of stretch
* Presence of irritants (cause us to sneeze!)
* Send messages to respiratory centre in the brainstem to influence respiratory rhythm - Sympathetic fibres
* Dilate bronchioles via relaxing smooth muscle - Parasympathetic fibres
* Constrict bronchioles via contracting smooth muscle
- changing bronchiole diameter alters resistance to air flow
Muscles of respiration
The diaphragm and the external intercostal musclesare the muscles used in quiet breathing. These are often referred to together as our “respiratory muscles”. These muscles contract during inspiration and relax during expiration.
The internal intercostal muscles only play a role in forced expiration only. During forced expiration, these muscles contract to decrease thoracic volume and increase pressure.
Expiration
- Involves muscle relaxation only
- Depends on recoil of the lungs (elasticity)
- Surface tension of the alveolar fluid
What stops the lungs collapsing?
- Surfactant reduces the surface tension of the alveolar fluid
- Pleural fluid “sticks” the parietal and visceral pleural membranes together
- Elasticity of the chest wall pulls the thoracic wall outwards
Passive vs Forced Expiration
Passive (quiet) expiration
involves muscle relaxation only (external intercostals and diaphragm) depends on lung recoil
Forced expiration
physical activity or specific vocalizations
internal intercostal muscles CONTRACT - further depress the ribcage involves contraction of accessory muscles:
eg. rectus abdominus - pull ribcage down, increase intra-abdominal pressure and push the diaphragm further upwards
Gas Flow / Ventilation
· In the conducting zone: air/gasses move down a pressure gradient via BULK FLOW
Gas flow through the lungs is dependant on a number of factors including:
- Resistance
- Alveolar surface tension
- Compliance
Resistance
- Gas flow = Pressure/Resistance (same as blood flow)
- Resistance = opposition to gas flow
- friction between air and airway walls
- dependant upon airway diameter
- neural control
Alveolar surface tension
Surface tension between water molecules in alveolar fluid
Surfactant – a lipid-protein complex produced by type II alveolar epithelial cells reduces surface tension of alveolar fluid
prevents alveolar collapse reduces effort required to expand alveoli - facilitates ventilation
Compliance
A measure of the ability of the lungs and/or thoracic cavity to stretch/ expand
Depends on:
* lung elasticity
* alveolar surface tension (surfactant production)
* flexibility of muscles and joints of the thoracic wall
External respiration (gas exchange at the alveoli)
- O2 diffuses from alveoli - pulmonary capillaries
- CO2 diffuses from pulmonary capillaries - alveoli
Internal respiration (gas exchange at the tissues)
- O2 diffuses from blood - tissues
- CO2 diffuses from tissues - blood
Oxygen transport
Problem = Oxygen is poorly soluble in water
Solution = erythrocytes (Red Blood Cells) + haemoglobin (Hb)
RBC are highly adapted for O2 transport:
* large surface area to volume ratio
* no organelles
* stackable and flexible
The chemical properties of Hb facilitate effective gas transport:
Lungs: O2 levels are high - Hb binds O2
Tissues: O2 levels are low - Hb releases O2
Carbon dioxide transport
- CO2 is a waste product
- Different ways of transporting CO2
PCO2 and pH are inversely related
when one variable is high, the other is low and vice versa
Hypoxia
Decreased oxygen at tissues
- homeostatic imbalance (flashback to week 1)
Cyanosis – blue tinge to skin and mucosa (mouth and nail beds)
Causes of hypoxia:
* Anaemia: too few RBC or decreased Hb
* Ischemia: blood circulation is reduced/blocked
* Hypoxemia: reduced PO2 in blood (respiratory disease, decreased atmospheric O2 )
Neural control of breathing
Respiratory centres (nuclei) in the brainstem set the respiratory rhythm
* Respiratory rhythm = the rate and depth of breathing
* neurons ‘fire’ in a cyclical manner to generate the repetitive cycle of inspiration: expiration
* neurons innervate the diaphragm and intercostal muscles
Factors that influence the respiratory centers/nuclei
- Stretch/inflation of the lungs – via stretch receptors
- Emotions (eg angry, frightened, excited) – via the limbic system and hypothalamus
- Choice (voluntary control) – controlled by primary motor cortex
Changes in CO2 and O2 are detected by chemoreceptors
Central chemoreceptors:
Located in the brainstem detect changes in CO2 levels
Peripheral chemoreceptors:
Located in the aortic arch and carotid sinuses and detect changes in CO2 , H+ and O2 levels
The effect of altered PO2
- Under normal conditions (PO2 95-104 mm Hg)
- O2 provides little stimulus for respiration O2 only becomes an important driver for ventilation when PO2 is very low (e.g. hypoxia
- Small increases in blood PCO2 cause large increases in ventilation
- Decreased blood PCO2 depresses breathing
- Small fluctuations in arterial PCO2 have large affects on breathing
